Process for making a multileveled electronic package

ABSTRACT

A multilevel electronic package comprising at least two levels, each level including a poly(aryl ether benzimidazole), a polymide and copper. A process of preparing this package is disclosed. Several novel poly(aryl ether benzimidazoles) useful in preparing this package are also set forth.

This is a divisional of application Ser. No. 08/318,392, filed on Oct.6, 1994, now U.S. Pat. No. 5,516,874, which is a continuationapplication of U.S. Ser. No. 08/268,422, filed on Jun. 30, 1994, nowabandoned.

BACKGROUND OF THE DISCLOSURE

1. Field of the Invention

The present invention is directed to an electronic multilevel packagewhich includes a poly(aryl ether benzimidazole), a polyimide and copperand a process for making same. In addition, the present invention isdirected to new species of poly(aryl ether benzimidazoles) which areemployed in the formation of multilevel electronic packages.

2. Background of the Prior Art

Electronic packaging is commonly employed in electrical and electronicdevices, assemblies, subassemblies, systems and the like. Usually,electronic packaging involves a multiplicity of layers, each layer ofwhich includes one or more electrical circuits. Most commonly, a circuitor circuits is formed by copper wiring or metal deposition disposed on alayer of a polyimide which, in turn, is disposed upon a substrate.

In forming multilayer electronic packages a first polyimide precursor isdisposed upon a substrate. That layer is thereupon cured to a polyimide.A patterned copper layer, defining an electrical circuit is embeddedinto the polyimide cured layer. The copper layer may be raised above orat the height of the polyimide where it is referred to as raised orplanar, respectively. This procedure is repeated to form themultilayered package.

Although the use of these materials are most appropriate to thisapplication, there are problems associated with their use. For one thingadhesion between copper and polyimides is poor. For another, copperreacts with polyimide precursors to form a fine precipitate of copperoxide particles within the polyimide layer. These two problems can bedisastrous in electronic application insofar as both of these problemscan lead to failure of the circuit. That is, poor adhesion can easilylead to discontinuity in the copper circuit based on the dislodging ofall or part of the copper conduit paths. Similarly, the inclusion offree copper oxide particles increases the electrical conductivity of thepolyimide which also leads to malfunction.

Many proposed solutions have been advanced to overcome these wellunderstood problems. One such solution, advanced to overcome thereactivity and poor adhesion between copper and polyimides problems, isto contact these materials with chromium.

When chromium is employed in a copper-polyimide planar layer, a chromiumlayer is disposed thereover which prevents contact between the copper onthe first layer with the polymide in the second layer. This results in achromium-polyimide interface and because, as those skilled in the artare aware, there is good adhesion between chromium and a polyimide, theadhesion problem is alleviated. Moreover, chromium does not react withpolyimides. As such, no reaction product of a chromium-containingcompound is formed to disturb the electrical insulation between thelayers.

Although this expedient is effective it is time consuming and expensive.It is even more time consuming and expensive when raised copper layersare involved. To cover the copper-polyimide layers, chromium must besputter coated to provide a thickness of 200Å to 500Å followed bycoating thereupon of the next polyimide layer. As those skilled in theart are aware, this involves the laying down of a film of a polyamicacid which thereupon is cured to form the polyimide.

An alternative to coating with chromium is to coat with tantalum.However, this change merely represents the substitution of one metal foranother. The time duration, the complexity and the expense of thisoperation is unchanged.

Yet another solution is provided by the introduction of an electrolessmetal, usually nickel, to coat the copper and provide a barrier to itscontact with the polyimide layer. This coating operation is technicallydifficult and is therefore costly. Moreover, the use of an electrolessmetal coating is oftentimes associated with an additional coating step,the coating of a silane coupling agent, which increases the complexityand expense of this alternative.

Other methods of overcoming the difficulties of copper-polyimide contactin multilevel electronic packages are provided by U.S. Pat. No.3,770,573 to Lindsey and U.S. Pat. No. 3,361,589 to Dumphy et al. Thesepatents, which are incorporated by reference, describe methods ofchemically treating the surface of polyimide film layers which improvetheir adhesivity.

Other proposed solutions have been advanced. Suffice it to say, thesesolutions involve the use of adhesion promoting agents which suffer fromincompatibility between their thermal, mechanical and/or electricalproperties and those of the polyimide layers with which they are incontact.

For example, U.S. Pat. No. 4,048,005 to Nakagome et al. describes aprocess for producing a heat resistant laminated metallic sheet composedof mutually insulated outer metallic sheets or foils disposed between aninner binder layer of a film of a heat resistant heterocyclic polymerfrom which the volatile matter is substantially removed. Theheterocyclic polymer may be a polyimide, a polyamide-imide, apolybenzimidazole, a polyhydantoin, a polyparabanic acid, a polythiazoleor a polyimidozopyrrolidone.

Not only does the generalized nature of the polyimides within thecontemplation of Nakagome et al. not specifically describe theparticular polyarylene ether benzimidazoles of the present inventionbut, moreover, there is no disclosure of utilizing the polymers of thispatent as an adhesive layer disposed between copper circuitry and anadjacent polyimide layer.

U.S. Pat. 5,180,639 to Zarnoch describes a method of modifying anaromatic polymer surface to improve the adhesion of that surface to ametal layer thereon. As such, this method is similar to the concept thathas been suggested for overcoming the problems associated with pooradhesion between copper and polyimide layers.

Although the Zarnoch patent involves a method of modifying an aromaticpolymer surface to improve the adhesion to a metal layer, the aromaticpolymers described in Zarnoch are primarily polycarbonates which aresubjected to nitration. The complexity of including chemical reaction,the nitration step, in the formation of the modified surface makes thisprocess of this patent unfavorable.

U.S. Pat. No. 4,022,649 to Nakagome et al. discloses a method ofproducing a metal laminate which includes a polybenzimidazole layer.Although this patent deals with heterocyclic polymers of the typeutilized in the present invention, the polymers utilized in the '649patent are not used to cap the copper layer to prevent copper fromreacting with polyamic acid. Thus, the '649 patent does not provide ateaching which results in enhanced adhesion of copper to polyimide.

U.S. Pat. No. 5,120,819 to Lubowitz et al. sets forth a class ofcrosslinkable oligomers that include oxazole, thiazole or imidazolelinkages. It is emphasized, however, that the '819 patent does notdisclose or suggest the use of the oligomers taught therein in thecapping of copper. Neither does it disclose or suggest a process ofmanufacturing a multilayered electronic package.

U.S. Pat. No. 3,533,879 to Levine describes a process wherein fusiblepolybenzimidazoles impregnate fabrics permitting the formation of fabriclaminates and the like. This patent provides no disclosure relating toan electrical multilayered article.

U.S. Pat. No. 3,957,726 to Gordon et al. discloses novel polyimideswhich polymers are described as useful in the formation of prepregs andlaminates. None of the polymers, prepregs, films and laminates,disclosed as useful in the formation of prepregs and laminates, aredescribed in Gordon et al. for use in the capping of copper, essentialin the formation of multilayered electrical packages.

The above remarks establish the need in the art for a new multileveledelectronic package and a process for forming the same, which insuresadhesion of copper and which also is free of the problem associated withthe formation of copper-containing precipitates, to thus minimizedegradation of the dielectric in multilayered electronic packages.

SUMMARY OF THE INVENTION

A new multilayered package and a process for forming that package,useful in electronic multilevel packages, which eliminates the problemsof precipitation of copper oxide and other copper-containingprecipitates as well as poor adhesion of copper to a dielectric surface,has now been discovered. New polymers, furthermore, useful in overcomingthese problems, associated with copper-polyimide interfaces in the priorart, have also been discovered.

In accordance with the present invention, a multilevel package, usefulin microelectronic applications, is provided. The multileveledelectronic package comprises at least two levels, each level including apolyimide, a poly (aryl ether benzimidazole) and copper.

In further accordance with the present invention, new poly(aryl etherbenzimidazoles) useful in the manufacture of the aforementionedmultilayered structure is set forth. These poly(arylene etherbenzimidazoles) include those having the structural formulae ##STR1##where m is an integer of at least about 2. ##STR2## where x is at leastabout 0.1; y is at least about 0.1; with the proviso that the sum of xand y are at least about 1; and z is an integer of at least about 15;##STR3## where X is ##STR4## and p is an integer of at least about 15.

In further accordance with the present invention a process is providedfor preparing a multilevel electronic package comprising disposing alayer of a solution of a poly(aryl ether benzimidazole) in an aproticsolvent over a substrate. This layer is heated to drive off the aproticsolvent. A coating of a polyamic acid is next added to the layer of thepoly(aryl ether benzimidazole). The poly(aryl ether benzimidazole) iscured as is the polyamic acid which is chemically converted to thecorresponding polyimide. Vias are formed in this cured product andcopper is deposited therein to complete the formation a first level. Atleast one additional layer, initiated by the depositing of a solution ofa poly(aryl ether) benzimidazole atop the first layer, is included inthis process.

DETAILED DESCRIPTION

The multilayered package of the present invention is characterized bygood adhesion between a dielectric and copper without the attendantproblem, associated with formation of free compounds of copper,especially copper oxides, in the multilayered electronic packages of theprior art. This package includes, in addition to a polyimide dielectricand a copper conductor, a poly(aryl ether benzimidazole). Many of thesepoly(aryl ether benzimidazoles) are themselves novel. However, the useof any poly(aryl ether benzimidazole) in a multileveled electronicpackage with a polyimide and copper is new.

The advantage provided by employing a poly(aryl ether benzimidazole)with copper and a polyimide in this application resides in its adherenceto both polyimides and copper to thus overcome the well known pooradhesion between copper and polyimides. Furthermore, poly(aryl etherbenzimidazoles) provide a barrier between the polyimide precursor(polyamic acid) and copper during formation of multilevel packages toprevent formation of copper oxides. Thus, the presence of poly(arylether benzimidazoles) overcome the two principal problems associatedwith electronic multilevel packages of the prior art. Specifically, theabove remarks explain how the bonding problem between polyimides andcopper as well as the problem of the reaction of polyamic acid andcopper is overcome by the disposition therebetween of a layer ofpoly(aryl ether benzimidazole) in the manufacture of multileveledpackages. That is, the multilevel package manufacturing processeliminates, in the second and subsequent layers, contact between copperand polyamic acid.

In the present invention a multilevel electronic package is provided inwhich each level includes a poly(aryl ether benzimidazole), a polyimideand copper. Examples of multilevel packages include multichip modules,printed wiring boards, integrated circuit chips and backend of chips.

In preparing the multilayered package of the present invention, a newprocess is provided which includes a first step of disposing a coatingof a poly(aryl ethyl benzimidazole) (PAEBI) upon a substrate. The PAEBIis provided in the form of a solution, usually in aprotic solvent, suchas N-methyl pyrrolidone (NMP), dimethylpropylene urea (DMPU), cyclohexylpyrrolidone (CHP), mixtures thereof and the like.

Although any PAEBI may be employed in the preparation of the package ofthis invention, certain specific PAEBI polymers are preferred. Many ofthese preferred polymers are new in the art.

One preferred PAEBI is the polymer having the structural formula##STR5## where n is an integer of at least about 15.

The PAEBI having the structural formula I is disclosed in Smith et al.,Polym. Prepr., 32 (3), 193 (1991). This preferred species of PAEBI isformed by reacting a stoichemetric excess of1,3-bis(4-fluorobenzoyl)benzene with5,5'-bis-2-(4-hydroxylphenyl)benzimidazole in the presence of anhydrouspotassium carbonate in dimethyl acetate, preferably at 18% solids. Inaddition to the above reactants, 2-(4hydroxyphenyl)benzimidazole is usedto endcap the polymer and is added at the beginning of the reaction.

Another PAEBI within the contemplation of the present invention is onehaving the structural formula ##STR6## where m is an integer of at leastabout 2. More preferably m is an integer of between about 5 and about15.

The PAEBI having the structural formula II is prepared by reacting1,3-bis(4-fluoro-benzoyl)benzene with5,5-bis(2-(4-hydroxyphenyl)benzimidazole in the presence of4-hydroxyphenylacetylene at a temperature in the range of between about140° C. and about 150° C. in a solution of dimethyl acetate (DMAc) andtoluene under an inert atmosphere of nitrogen. The reaction furthermoreoccurs in the presence of a mild base, preferably amorphous potassiumcarbonate.

The new PAEBI having the structural formula II, although similar to thePAEBI having the structural formula I, insofar as it shares the physicalcharacteristics of good thermal stability, low residual stress fromthermal cycling, high modulus and elongation and exceptional adhesion toboth polyimides and copper, the polymer having the structural formula IIhas an improved property provided by its end cap groups. That is, theacetylenic bonds therein permit easy crosslink curing by thermal means.This easy crosslinking enhances the cured polymer's mechanicalproperties.

Another PAEBI which may be utilized in the multilevel electronic packageof the present invention is the copolymer having the repeatingstructural unit ##STR7## where x is at least about 0.1; y is at leastabout 0.1, with the proviso that the sum of x and y is at least 1; and zis an integer of at least about 15. Preferably, x is about 0.6 to about0.8; y is between about 0.2 to about 0.4; and z is an integer of betweenabout 20 and about 30.

The PAEBI polymer having the structural formula III is prepared byreacting 1,3-bis(4-fluorobenzoyl)benzene with5,5'-bis-2-(4-hydroxyphenyl)benzimidazole in N-methyl pyrrolidone (NMP)and anhydrous K₂ CO₃, similar to the method used to polymerize the PAEBIhaving the structural formula I. However, these polymerization reactantsare supplemented with the inclusion of the compounds, Bisphenol-6F and4,4'-difluorobenzophenone.

The polymer having the structural formula III provides an improvementover the PAEBI of formula I. That is, the copolymer of formula III haslower water uptake than does the PAEBI of formula I. Whereas the PAEBIof formula I has a water uptake of up to about 4% by weight, the wateruptake of the PAEBI copolymer having the structural formula III is onlyabout 0.4% by weight.

As those skilled in the art are aware, water has an adverse effect onthe properties sought to be provided in the electronic multileveledpackage of the present invention. Specifically, water in PAEBI polymersreduces the polymer's adhesivity to other polymers and metals andreduces its barrier properties, permitting interaction between copperand polyimides.

Additional PAEBI polymers, useful in the multileveled electronicstructure of the present invention, which are themselves new are thepolymers having the structural formula ##STR8## where X is ##STR9## andp is an integer of at least about 15.

The PAEBI's having the structural formula IV are more soluble in aproticsolvents, such as NMP, DMPU and CHP, than are the earlier PAEBI'sfacilitating their utilization in multilevel electronic packages.

Polymers defined by structural formula IV are prepared by reacting2,2'-bis(fluorophenyl)-6,6'-bibenzimidazole with the appropriatereactant, which defines the meaning of X, in the repeating structuralunit. Thus, such bisphenols as Bisphenol A, Bisphenol AF bis(6-hydroxyphenyl)diphenylmethane and 9,9'-bis(hydroxyphenyl)fluorene maybe employed. In addition, other reactants such as hydroquinone,resorcinol, dihydroxdiphenylsulfone and dihydroxylbenzophenone may alsobe used instead of the above mentioned bisphenols. This reaction occursin an aprotic solvent in the presence of anhydrous potassium hydroxideas a base.

The product polymer having the structural formula IV is a high molecularweight polymer having an inherent viscosity of about 0.4 deciliters pergram and have a glass transition temperature in the range of betweenabout 230° C. and about 260° C. However, these polymers are soluble inNMP up to as high a solids content as about 15% to about 25% by weight.

The PAEBI, disposed in solution form upon a substrate, is thereuponsubjected to elevated temperature to drive off the solvent, usuallycomprising an aprotic solvent. Preferably, the PAEBI solution is exposedto a temperature of between about 70° C. and about 200° C. atatmospheric pressure. More preferably, this temperature is in the rangeof between about 85° C. and about 150° C.

The thus formed PAEBI layer is thereupon overcoated with a layer ofpolyamic acid. Polyamic acids are prepared as the product of acondensation reaction between a dianhydride and a diamine.

Polyamic acids may also be prepared as the condensation reaction betweena diester-diacid or a diester-diacid dichloride and a diamine.Additionally, polyamic acids can be formed by the condensation reactionbetween a dianhydride and a diisocyanate. Other methods of preparing apolyamic acid, which, as will be discussed below, is a polyimideprecursor, include the reaction of bis(carboethoxy)diimide with adiamine and the electrochemical reaction of aminophthalic acid.

Other methods of preparing polyimide precursors are provided inKirk-Othermer, "Encyclopedia of Chemical Technology, Third Edition,"Vol. 18, pp. 704-719 and the aforementioned U.S. Pat. No. 3,361,589 toLindsey and U.S. Pat. No. 3,770,573 to Dumphy et al., all of which areincorporated herein by reference.

Polyamic acids are converted to the corresponding polyimide by beingcured at elevated temperature. Usually, exposing a polyamic acid to atemperature in the range of between about 300° C. and about 400° C. atatmospheric pressure effects its curing to form a polyimide.

This temperature range also effects curing of PAEBI polymers. Therefore,the polyamic acid and PAEBI, disposed on the substrate, is subjected toheating in this temperature range resulting in the curing of thesepolymers. It is emphasized, however, that the polymers are curedrandomly so that it cannot be said that distinct layers are formed, asin a classical laminate. Of course, this remote possibility is notexcluded.

The thus cured product is next subjected to the step of forming thedesired electrical circuit thereon. This is accomplished by lithographicmethods known in the art wherein the desired circuit is etched, cut orotherwise provided in the cured polyimide-PAEBI surface in the form ofvias. Finally, a first layer of the multileveled package is completed bydepositing copper into the vias by methods again well known in the art.

A second layer is then prepared by repeating the above process. Again afirst layer of a PAEBI in solution initiates the preparation. Theinstant process thus insures that the copper present in the first layeris not exposed to polyamic acid with which it reacts due to theprotective layer of PAEBI disposed over exposed copper before thesubsequent coating with a new layer of a polyamic acid. Furthermore, thepresence of PAEBI throughout the layer insures good adhesion to copper.As will be demonstrated to both copper and in the examples, PAEBI alsoexhibits good adhesion to both copper and polyimides.

The following examples are given to illustrate the present invention.Because these examples are given for illustrative purposes only, thepresent invention should not be limited thereto.

EXAMPLE 1 Preparation of a Material Containing Copper, a Polyimide and aPoly(aryl ether benzimidazole)

The surface of a thin copper foil was cleaned with dilute acetic acid.The cleaned copper surface was coated with a solution of a PAEBI havingthe structural formula I dissolved in a mixed cyclopentanone-NMP solventpresent in a weight ratio of 60:40. After a uniform 0.1 micron thicklayer of the PAEBI was disposed on the copper foil and soft baked at150° C., poly(biphenyl dianhydride-p-phenylene diamine) (BPDA-PDA) wascoated upon the PAEBI layer. The PAEBI and polyamic acid, i.e.(BPDA-PDA), were cured by exposure to a temperature of 85° C. for 30minutes followed by heating at a temperature of 150° C. for 30 minutes.The polymers were then heated for 30 minutes at 230° C., then for 30minutes at 300° C. and finally for 1 hour at 400° C.

EXAMPLE 2 Adhesivity of PAEBI to Copper

A 10 micron layer of copper was disposed over a substrate. The layerwas, in turn, coated with a solution of PAEBI having the structuralformula I dissolved in a 60:40 cyclopentanone-NMP solvent mixture andsoft baked at 150° C. for 1 hour. A layer of BPDA-PDA was disposed ontothe PAEBI layer, as in Example 1, and then the two polymers weresimultaneously cured in accordance with the procedure set forth inExample 1.

The result was a cured polymeric layer, 20 microns thick, disposed overthe 10 microns thick copper layer. Since the PAEBI layer was separatelyapplied prior to the polyamic acid, two layers formed in the 20 micronthick polymer layer. Because PAEBI was initially disposed over thecopper layer it was the bottom layer, in contact with the copper layer.

Sample strips 5 mm wide were cut from the thus formed structure. Thepolymeric layer was peeled from the copper layer employing an Instron[trademark] machine by a method well known in the art. Upon the testingof several samples it was determined that the peel strength, required toseparate the PAEBI layer from the copper layer, ranged from 80 to 90g/mm. That is, statistical analysis established this range to representthe quantitative adhesivity between PAEBI and copper.

EXAMPLE 3 Adhesivity of PAEBI to a Polyimide

A cured 10 micron layer of the polyimide utilized in Examples 1 and 2was formed on a substrate by thermal curing in accordance with theprocedure mentioned therein. The cured polyimide layer was subsequentlymodified with KOH followed by modification with acetic acid, then rinsedwith water and isopropyl alcohol to produce a 10 micron thick layer ofthe cured polyimide.

Thereupon, 20 micron thick layer of cured PAEBI and polyimide, identicalto that disposed over the 10 micron thick copper layer in Example 2, wasprepared in an identical manner to the preparation of that layer inExample 2.

As in Example 2, the fact that PAEBI was the first applied polymer overthe cured polyimide resulted in the PAEBI layer being disposed atop the10 micron polyimide layer. Thus, the adhesivity of PAEBI to polyimidewas determined again by measurement of The peel strength required toseparate these layers.

That is, in identical fashion to Example 2, an Instron [trademark]machine was employed to measure the force required to peel 5 mm stripsamples of adjoining polymeric layers. It was found that the peelstrength of PAEBI to polyimide was, over the average of several samples,98 g/mm.

EXAMPLE 4 Diffusion Barrier Characteristics of PAEBI

A cross section of the copper-polymer interface of a cured sample ofExample 2 was investigated using Transmittance Electron Microscopy(TEM). It was found that the polymer contained no copper-containingprecipitate. It was thus concluded that PAEBI, disposed between thecopper and polyimide layers, acted as a barrier preventing contactbetween the layers which it separated.

EXAMPLE 5 Preparation of the PAEBI Having the Structural Formula II

1,3-Bis(4-fluorobenzoyl)benzene was reacted with5,5'-bis(2-(4-hydroxyphenyl)benzimidazole) in the presence of4-hydroxyphenyl acetylene. This polymerization reaction occurred in thepresence of a DMAc-toluene mixed solvent under a temperature of 155° C.and in the presence of potassium carbonate.

The resultant product, PAEBI having the structural formula II.

EXAMPLE 6 Preparation of the PAEBI Having the Structural Formula III

1,3-Bis(4-fluorobenzoyl)benzene was reacted with Bisphenol AF in thepresence of 4,4'-difluorobenzophenone. This reaction took place in anNMP solution at a temperature of 175° C. at atmospheric pressure.

The product of this reaction was a polymer having the structural formulaIII. This polymer was characterized by an intrinsic viscosity of 0.45deciliter per gram, as measured at 25° C. in NMP.

EXAMPLE 7 Preparation of PAEBI's Having the Structural Formula IV

2,2'-Bis(fluorophenyl)-6,6'-bibenzimidazole was separately in BisphenolAF, bis(6-hydroxyphenyl)-diphenylmethane,9,9'-bis(hydroxyphenyl)fluorene and Bisphenol A. Each of these reactionstook place in a dimethylpropylene urea and/or mixedN-methylpyrrolidonecyclohexyl pyrrolidone solution.

The polymeric product of these reactions had the structural formula IVwhere X has the meanings given in Table 1 below. Table 1 also includesthe characterizing physical properties glass transition temperature andintrinsic viscosity, measured in NMP at 25° C., for the PAEBI products.

                                      TABLE 1                                     __________________________________________________________________________    Bisphenol         Poly. Solvent                                                                         X                     Tg, °C.                                                                     [Tg].sup.25°                                                           C. NMP                   __________________________________________________________________________                                                         dl/g                     Bisphenol AF Bisphenol AF                                                                       DMPU NMP/CHP                                                                           ##STR10##            218  0.45 0.46                bis(6-hydroxyphenyl)diphenylmethane bis(6-hydroxyphenyl)diphenylmethane                         DMPU NMP/CHP                                                                           ##STR11##            228  0.36 0.44                9,9'-bis(hydroxyphenyl)fluorene 9,9'-bis(hydroxyphenyl)fluorene                                 DMPU NMP/CHP                                                                           ##STR12##            250  0.43 0.44                Bisphenol A       NMP/CHP                                                                                ##STR13##                 0.38                     __________________________________________________________________________

The above embodiments and examples will make apparent, to those skilledin the art, other embodiments and example. These other embodiments andexamples are within the contemplation of the present invention.Therefore, the present invention should be limited only by the appendedclaims.

What is claimed is:
 1. A process of making a multileveled electronicpackage comprising the steps of:(a) depositing a layer of poly(arylether benzimidazole), in the form of a solution, over a substrate; (b)heating said poly(aryl ether benzimidazole) layer to drive off saidsolvent; (c) adding a coating of polyamic acid to said layer of saidpoly(aryl ether benzimidazole) whereby a product is formed; (d) heatingsaid product of step (c) whereby said poly(aryl ether benzimidazole) iscured and said polymeric acid is converted to a cured polyimide toprovide a randomly cured product; (e) forming vias in said randomlycured product of step (d); (f) depositing copper in said vias tocomplete a first layer; and (g) repeating steps (a) to (f) whereby asecond layer is formed.
 2. A process in accordance with claim 1 whereinsaid step (d) of heating poly(aryl ether benzimidazole) and saidpolyamic acid to form said cured polyimide occurs at a temperature ofbetween about 300° C. and about 400° C.
 3. A process in accordance withclaim 2 wherein said solvent of said poly(aryl ether benzimidazole)solution in said step (a) includes an aprotic solvent.
 4. A process inaccordance with claim 3 wherein said heating step (b) occurs at atemperature in the range of between about 70° C. and about 200° C.
 5. Aprocess in accordance with claim 1 wherein said poly(aryl etherbenzimidazole) has the structural formula ##STR14## where n is aninteger of at least about
 15. 6. A process in accordance with claim 1wherein aid poly(aryl ether benzimidazole) has the structural formula##STR15## where m is an integer of at least about
 2. 7. A process inaccordance with claim 1 wherein said poly (aryl ether benzimidazole) hasthe structural formula ##STR16## where x is at least about 0.1; y is atleast about 0.1, with the proviso that the sum of x and y is at leastabout 1; and z is an integer of at least about
 15. 8. A process inaccordance with claim 1 wherein said poly(aryl ether benzimidazole) hasthe structural formula ##STR17## where X is ##STR18## and p is aninteger of at least about 15.